Dynamically adding Parts to ContentType

Can someone shed some light as to how I can add Parts to a known contentType programmatically without giving hard references to the Parts?

For eg, I know that Parts can be associated to ContentType in the Handler class via:
Filters.Add(new ActivatingFilter<SomePart1>("MyContentType"));
Filters.Add(new ActivatingFilter<SomePart2>("MyContentType"));

So this is essentially associating MyContentType with SomePart1 and SomePart2.
What I want is, not to give some concrete type so I can associate them dynamically at runtime ?
Maybe, ActivatingFilter("SomePart1","MyContentType") ?